This invention relates to a divided flywheel for reducing the transmission of vibrations from an engine to a power transmission line. The flywheel has two coaxially arranged flywheel parts which are limitedly and mutually rotatable, one of which is drivingly connected to the engine and the other to the transmission line. A coupling spring arrangement is disposed between the flywheel parts and tends to return the parts from mutually rotated positions into a central position. An attenuation arrangement limits the amplitudes of resonant vibrations of the flywheel parts on the transmission line side. The masses of the flywheel parts and the relative rigidity of the coupling springs are designed such that the frequency of the resonant vibrations is lower than the frequency of the engine vibrations during operation above a threshold value of the engine speed.
A flywheel of this type is described in German Unexamined Patent Application No. 2,358,516. As soon as the engine speed exceeds the threshold value sufficiently, it becomes virtually impossible for any engine vibrations to be transmitted to the transmission line, because due to the interposed coupling spring means, the engine-side flywheel part cannot transmit the engine vibrations, or can transmit them only greatly attenuated, to the transmission line side flywheel part. In this so-called supercritical range, a vehicle is therefore characterized by extraordinarily quiet running and freedom from vibrations in the transmission line.
However, when starting the engine, passing through a speed range in which resonances occur cannot be avoided, so that the transmission line-side flywheel part may possibly vibrate with a substantially greater amplitude than the engine-side flywheel part. Such resonant vibrations must be suppressed by intense attenuation.
At the same time, however, it is noted that an intense attenuation is undesirable in the super-critical range, because this would result in the intensified transcoupling of engine vibrations to the transmission line.
In German Patent Application No. 2,358,516 (see FIG. 6), an annular part is provided, resiliently and concentrically, on the transmission line-side flywheel part. The masses of the transmission line-side flywheel part and of the annular part, and the intensity of the spring means between these two parts are selected so that the above-mentioned resonant vibrations of the transmission line-side flywheel part are suppressed, because the annular part constitutes a dynamic attenuator.
The divided flywheel according to German Patent Application No. 2,358,516 accordingly constitutes, in principle, a three-part flywheel, the parts of which are mutually and resiliently connected. However, such a vibrating system with three vibrating masses is complicated to design and difficult to control. Furthermore, resonant vibrations may possibly be produced during operation in the supercritical range.
It is therefore an object of this invention to provide a divided flywheel which is characterized by its relatively simple design, and which operates in a relatively simple manner, while decoupling the transmission line from engine-side vibrations in the so-called supercritical range in a particularly efficacious manner.
These and other objects are attained in a divided flywheel which includes an input part connected to an output of an engine and a coaxial output part connected to the input of the power train or transmission line. The parts are coupled by a coupling spring arrangement disposed therebetween. A degree of relative rotation of the parts is allowed by this coupling arrangement. In a preferred embodiment, the assembly further includes a connecting part which is frictionally attached to one of the parts, and which engages the other of the respective parts following relative rotation of the parts through a first predetermined angular displacement. Following engagement, this arrangement offers resistance to further relative displacement of the parts. The preferred embodiment also includes a stop spring arrangement on one of the parts which engages a stop on the other of the parts following a further relative displacement through a second predetermined angular distance. For relative rotation in excess of the second predetermined displacement, a portion of the connecting part is clamped between the stop spring and the stop to further enhance the attenuation of vibrations.
The flywheel according to the present invention therefore has two flywheel parts which are mutually coupled in supercritical operation almost exclusively by the coupling spring means with low or virtually negligible attenuation. It is therefore virtually impossible for any vibrations to be transmitted from the engine to the transmission line.
Neither the connecting part nor the stop spring means take effect for the relatively low vibration amplitudes which occur in the supercritical operating range.
On the other hand, when passing through the resonant range of the vibrating system formed by the flywheel parts and the coupling spring means--when starting the engine, for example--greater amplitudes of vibration occur and the two flywheel parts are mutually displaced comparatively far. One flywheel part then initially moves the connecting part by virtue of a non-positive coupling, until its play relative to the other flywheel part is exhausted. In the event of further relative displacement of the parts, one part is moved against the resistance of the non-positive connection existing between the above-mentioned flywheel part and the connecting part, because the connecting part can no longer follow the movement of the one flywheel part due to the exhaustion of the play. The relative movements of the two flywheel parts are accordingly attenuated. Furthermore, in the case of further relative displacement of the flywheel parts, a stop spring means braced against one flywheel part and a stop arranged on the other flywheel part approach each other. Ultimately, the connecting part, or a part arranged thereon, becomes clamped between the stop spring means and the stop. Accordingly, for further relative displacement to occur, the flywheel parts must overcome the force of the stop spring means and the attenuation resistance caused by the non-positive connection between one flywheel part and the connecting part and the force of the coupling spring means. Excessive relative movement of the flywheel parts is therefore effectively limited, due to an intensified attenuation between the flywheel parts and to a change in the resonant frequency caused by cooperation of the stop spring means and the compling spring means from that which would exist if the coupling springs were used exclusively.
The clamping of the connecting part, or of a part attached to the connecting part, between the stop and the stop spring means further assures that the non-positive attenuation between one flywheel part and the connecting part is effective in both directions near the point of reversal of the relative movement of the flywheel parts. When the direction of relative movement between the flywheel parts reverses, the connecting part, or the part attached thereto, initially remains clamped between the stop and the stop spring means, so that--in spite of the above-mentioned play--the connecting part is unable to move relative to the other flywheel part. Consequently, the movements of the one flywheel part can occur only against the resistance of the non-positive connection between this flywheel part and the connecting part.
According to a preferred embodiment of the invention, the stop spring means may optionally be arranged asymmetrically and consequently take effect for a relatively slight displacement of the flywheel parts in one direction, but only for relatively large displacements of the flywheel parts in the other direction. In this case, an asymmetrical arrangement is generally employed such that when the vehicle or other machine accelerates, the flywheel parts tend to be relatively displaced in the direction in which the stop spring means takes effect only for relatively large displacement angles.
The play between the connecting part and one flywheel part is generally smaller than the play between the stop spring means on one flywheel part and the stop arrangement on the other. In this way it is ensured that the attenuation caused by the non-positive connection between the connecting part and one flywheel part, when the play between these parts is exhausted, takes effect before the stop spring means contacts the stop arrangement.
However, it is also possible for the play between the connecting part and the flywheel part to be approximately equal to the play between the stop arrangement and the stop spring means. By this means, the attenuation caused by the connecting part takes effect simultaneously with the effect of the stop spring means.
It is also possible to arrange two connecting parts, which are respectively coupled frictionally to the same flywheel part, but which have a different amount of play relative to the other flywheel part. In this case, the play of one connecting part may correspond to the play between the stop spring means and the stop arrangement, whereas the play of the other connecting part is smaller.
Lastly, the flywheel parts may also be coupled additionally by means of an attenuator arrangement which also incorporates play, and which takes effect only for larger relative displacements of the flywheel parts. If the attenuation force is sufficiently intense, such an arrangement may be used alternatively to the stop spring means to achieve a particularly simple design.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.